Reference may be made to the following U.S. patents of interest: U.S. Pat. Nos. 2,517,150; 2,613,751; 2,689,010; 3,096,046; 3,228,629; 3,622,973; 3,659,236; 3,857,194; and German Pat. No. 1,965,871.
In full size as well as radio controlled model helicopters, vertical movements of the craft can be provided by either varying the main rotor rotational speed or by varying the main rotor collective pitch (the average incidence angle of all blades on the rotor). Horizontal, forward or reverse movements of a helicopter can be provided by variations in the main rotor pitch during rotation -- known as cyclic pitch. Undesired rotation of the helicopter fuselage can be provided by various techniques, one of which is to vary the collective pitch or the rotational speed of a tail rotor rotating in a plane orthogonal to the main rotor. The present invention is only concerned with controlling the vertical movement of a radio controlled model helicopter.
The pilot of a radio controlled model helicopter either has separate throttle and collective pitch controls on a radio transmitter unit, or more often, the two functions are coupled and controlled from a single throttle-collective control on the radio transmitter unit. The respective control signals are transmitted to and received by a receiver unit in the model helicopter. These control signals are then decoded for driving a respective throttle servo coupled to an engine for rotating the helicopter main rotor; or, for driving a collective pitch servo for varying the collective pitch in a known manner. In the case of a coupled throttle/collective system both throttle and collective operate from a single servo. Flying model helicopters is thus a delicate procedure requiring some degree of coordination between variations in the throttle and the collective pitch controls. If, for instance, the throttle were increased, the rotor speed would tend to increase, but at a high initial collective pitch the load on the rotor might become intolerable and the engine would start to stall. In the coupled system where both functions are on a single control, it becomes difficult to obtain correct mechanical relationship such that the proper amount of power is present for any given collective pitch setting.
In full size helicopters, rotor speed and rotor pitch governor systems have been utilized to aid in the coordination of the throttle and collective pitch functions. For instance, in a throttle governor system for full size helicopters, the throttle is adjusted in accordance with the speed of the main rotor so as to maintain a constant rotor speed, and the lift of the rotor is then controlled by varying the rotor pitch. In addition, in full size helicopters there has also been provided a collective pitch governor system wherein the pitch of the rotor is adjusted in accordance with the speed of the rotor to maintain substantially constant rotor speed, and the lift of the rotor is controlled by varying the throttle. The apparatus involved in such full size systems are obviously quite large and bulky and are not readily adaptable for use with small sized radio controlled model helicopter apparatus.
Attempts have been made in the prior art to provide some automatic correlation in the throttle and collective pitch controls for model helicopters. As an example, a mechanical coupling has been provided between the throttle and collective pitch controls, however, under some flight situations this interconnection becomes a hindrance rather than an aid. It is therefore desired to provide a workable system wherein a model helicopter pilot could fly the helicopter by varying either the throttle or the collective pitch control and the other respective control would be automatically controlled. This would make the automatically controlled function related to, but indirectly coupled to the manually controlled function.